In many bird species plasma testosterone rises when a male interacts with a female. In the ring dove (Streptopelia risoria) this neuroendocrine response occurs even when physical contact between male and female is prevented. Important details of this response remain to be clarified, however. Through the studies proposed here we expect to find the following: 1. The rise in plasma testosterone is simulated by the male's own vocal behavior as he courts the female. 2. Plasma testosterone will rise when a male dove is introduced to a human keeper or another species upon which he has been sexually imprinted. 3. The elevation in testosterone level is primarily attributable to increased activity of the left testis. (Preliminary evidence from our laboratory indicates that the left testis is relatively inactive in socially isolated male doves but that it equals the right testis in activity after the male is introduced to a female.) 4. The left and right testes of socially isolated males have different receptor characteristics. Implications: Recent evidence indicates that the immune system is influenced by testosterone. If we show that testosterone secretion is influenced by self-feedback from overt behavior, we shall have a model system for examining how an individual's own behavior can affect his resistance to pathogens. Second, if we show that neuroendocrine responses are affected by sexual imprinting, it may suggest that psychosexual orientation involves more of the total organism than is commonly recognized. Finally, if we confirm our observation of an asymmetrical testicular response, it may indicate that the two testes are performing different functions.